1. Field of the Invention
The present invention relates to an image forming apparatus and an image reading apparatus. In particular, the present invention relates to an image forming apparatus and an image reading apparatus for reading a document using so-called sheet-through scanning.
2. Description of Related Art
In recent years, in view of convenience for users, many models of image forming apparatuses (e.g., photocopiers) which adopt sheet-through scanning in addition to movable optical scanning are introduced into the market. In the movable optical scanning, a document is placed on a platen glass, and the stationary document is read by moving an optical system under the document. In the sheet-through scanning, a document is moved to pass through a reading position on a platen glass using an automatic document feeder (ADF), and the document is read by a stationary optical system under the platen glass.
In the image forming apparatus, the movable optical scanning and the sheet-through scanning are selectively used depending on the application. For example, the movable optical scanning is used for copying a document such as a book which is not suitably read using the ADF. The sheet-through scanning is used for copying a document comprising a plurality of sheets which can be fed one by one automatically.
When dust is attached to the platen glass, in both of the scanning methods, the dust is read together with document into an image. In the case of reading by the movable optical scanning, the dust is simply reproduced as a black point corresponding to the size of the dust. However, in the case of reading by the sheet-through scanning, the dust is reproduced as a black stripe extending from one end to the other end of the document image. The black stripe is hardly negligible.
In an attempt to address the problem, image reading apparatuses for reducing the occurrence of the black stripe in the presence of dust attached to the upper surface of the platen glass have been developed.
In an image forming apparatus disclosed in Japanese laid-open patent publication No. 2001-272829, at the time of reading the document (at the time of feeding the document by the ADF), the platen glass is moved in an secondary scanning direction (in a feeding direction of the document). According to the disclosure, even if dust is attached to the platen glass, the dust does not stay at the document reading position. As a result, even though it depends on the movement of the platen glass, the read dust is reproduced as a short line, for example. It is possible to at least avoid the situation in which the read dust is reproduced as a black stripe extending from one end to the other end of the document image, or it is possible to reduce the occurrence of reproducing such a black stripe.
In the apparatus having the above structure, since the platen glass is a movable member, it is necessary to suitably control the movement of the platen glass. Japanese laid-open patent publication No. 2001-272829 discloses basic operation of the platen glass. Specifically, during the operation sequence from the start of reading the document to the end of the reading, a reciprocal movement is made by moving the platen glass by a predetermined distance and moving the platen glass back to the home position. However, Japanese laid-open patent publication No. 2001-272829 does not disclose any movement control of the platen glass, e.g., when a jam of the document occurs in the ADF.
In view of the above, an object of the present invention is to provide an image forming apparatus and an image reading apparatus which makes it possible to suitably control movement of a platen glass depending on various situations.